Specific absorption rate (SAR) is a measure of the rate at which radio frequency (RF) energy is absorbed by a body when exposed to a radio-frequency electromagnetic field. SAR testing insures RF emitting products don't exceed government set limits. Wide spread use of cell phones and 802.11 devices have made the public aware of SAR and concerns regarding radiation absorption. Devices that emit RF energy that are intended to be worn for long periods of time can cause additional concern to the public. This concern might reduce the public acceptance of an otherwise successful product.
During SAR regulatory testing, a manufacturer must specify to the government the usage cases for the product. As an example, a mobile 802.11 device will emit much more radiation when the device is at the fringe of the access point coverage area. This is due to an increase in transmission retry count and increase in peak power output of the mobile device. The net increase for this case can be on the order of 100 times. Another concern occurs when other RF traffic in the area degrades the RF link due to collisions. A manufacturer must specify these worst cases when the SAR testing takes place. Additional testing can be performed with typical cases but the results quickly become less conclusive and accepted by the public.